Current operational fire behavior models are empirically based on fire spread through surface fuels and do not describe heating and combustion processes. Current physical models describe fire spread processes; however, the fire spread processes of heat exchange and ignition are assumed without an experimental basis. Advancements are hindered by a variety of factors, including a lack of a basic understanding of crown fire spread and spread thresholds, the implications of mountain pine beetle attack on crown fires, and fire and fuel dynamics of crown fire ecosystems.
RMRS Fire, Fuel, and Smoke Science Program scientists and collaborators have developed a research program for understanding how fire spread occurs with a focus on live fuels and active crown fire. Supported by the National Fire Decision Support Center, studies at the Rocky Mountain Research Station address the following questions:
Specific fire dynamics research investigations include:
Please visit http://firelab.org/project/fundamental-wildland-fire-spread-research for more information and to see videos of our experiments.
Laboratory experiments suggest that radiant intensities found in wildland fires are not sufficient to ignite fine fuel particles such as needles and grasses; however, flame convection provides the critical heating of particles to ignition. Other experiments show that the edges of turbulent flames are responsible for igniting fuel particles after subjecting them to intermittent heating and cooling over time scales of about 1/10th of a second.
Researchers discovered that the ignition of wood depends on a critical rate of converting solid mass to combustible gas similar to other substances (such as plastic). Ignition depends on the heat flux and wind flow, providing an improved definition of ignition and flammability limits.
Findings also indicate that live fuels, such as conifer foliage, can burn at moisture contents many times higher than dead fuels because they release moisture explosively compared to slow diffusion in dead fuels, and they contain large amounts of non-structural carbohydrates.
This body of research suggests a completely new approach to understanding and modeling fire spread that is based on an experimentally supported theory, creating new opportunities for developing models that can be used for fire management applications.